Cold retreading a truck tyre normally comprises removing the worn tread from the tyre, and applying a new tread to the tyre casing. Applying a new tread to the casing comprises winding a green-rubber intermediate strip or cushion and a precured tread strip (PCT) about the casing; and the casing is further cured in a curing vessel to achieve firm grip of the tread to the casing through the binding action of the cushion.
One example of a precured tread strip ready for application to a tyre casing is described in U.S. Pat. No. 5,277,727A1; and one example of a cold tyre retreading station implementing the above method is described in U.S. Pat. No. 6,368,439B1.
Before winding on the precured tread strip, the outer surface of the previously applied cushion is sprayed with a green-rubber and normalheptane (or other organic solvent) liquid (known as cement) to grip the tread strip to the green-rubber cushion and prevent detachment of the tread strip from the green-rubber cushion when winding the tread strip about the casing.
Cementing, however, has several drawbacks. Cement being volatile and potentially highly contaminating, it must be applied in a cementing booth, which is bulky, expensive, and normally insulated with rock wool (which is expensive to dispose of). Moreover, cement is stored in drums, which are also expensive to dispose of; the presence of cement between the cushion and tread strip, i.e. of a heterogeneous material interposed between two rubber layers, may impair performance of the retreaded tyre; and, given the highly contaminating nature of the organic solvents in cement, avoiding the use of organic-solvent-based cement would greatly reduce the overall environmental impact of the tyre retreading process. In this connection, it is important to note that a recent European Union directive (VOC 13/1999/EC) calls for a 75% reduction in the use of organic solvents in industrial processes by the year 2007.
U.S. Pat. No. 5,635,015A1 describes a tyre retreading method in which, to avoid using cement, the green-rubber cushion is heated before being wound about the tyre. Heating the green-rubber cushion should improve its grip sufficiently to avoid using cement, but has been found to also soften it, thus making it more difficult to wind about the tyre. Moreover, the improvement in grip of the green-rubber cushion by heating it is not always sufficient to prevent detachment of the tread strip from the green-rubber cushion when winding the tread strip about the tyre.